A device with the features described above is known from the Jul. 29, 1994 issue of VDI Nachrichten and is used in hip operations. Before the operation, three screws are initially implanted into the patient's knee and the thigh bone. The screws have a slight indentation into which fits the head of a feeler arranged at the end of a robot arm. A computer tomograph also carried out before the operation provides necessary patient data for the program control system. During the surgical procedure, the patient's thigh is clamped in a sterile holder arm that is rigidly attached to the foot of the industrial robot. A measuring arm placed on the bone records any positional changes. Firstly, the surgeon leads the robot arm with the feeler at its end to the reference points given by the indentations in the screws, the coordinates of which are compared with the data from the tomograph. From the data, the computer then determines the working position of the robot arm for the surgical procedure. Once the working position has been determined, the feeler is replaced by an instrument and the femur shaft is milled using appropriate feed movements of the robot arm under program control. Next, the surgeon can insert a previously selected prosthesis.
The application of the known device requires extensive preoperative planning and use of computer tomography, which are not only expensive, but also prolong the operation time to an overall extent that is problematic. Also unfavorable is the fact that the surgeon has no possibility of exerting an influence on the program-controlled course of the operation. In the event of positional changes of the bone and/or non-compliance with predetermined tolerances, the device immediately interrupts its work for safety reasons.